Our Solar System -- Supernovas, collisions, toxic atmospheres!

This week, we focused on our own solar system.  Based on observations through telescopes, mathematical calculations, and other information, astronomers think the solar system formed about 4.5 billion years ago.  Our galaxy, the Milky Way, formed about 9 billion years ago, and the Big Bang at the beginning of time was about 14 billion years ago.

Our solar system was formed when a big cloud (called a nebula) of space debris started to collapse together and spin.  The most important thing that happened before that was that other stars had formed and become supernovas.  This means they got really hot and exploded, and that

• created the cloud of debris that then became our solar system
• made all the heavier elements in our solar system (the first stars were made up of mostly hydrogen and helium, and a little lithium, and only from supernova explosions were heavier elements created)
• sent shockwaves out that caused the cloud of debris to start collapsing and forming our solar system

This is a real supernova explosion

Stars become supernovas and explode all the time.  People looking through telescopes at home sometimes find them, when they notices a star suddenly become brighter.  The whole thing takes about 3 weeks for us to observe.

The sun will not become a supernova, because it doesn't have enough mass, but it is expanding and will make Earth uninhabitable in about a million years.

When our solar system formed, the planets began to orbit around the sun and also rotate.  The time it takes to go once around the sun (orbit time) is what we call a year.  The time it takes to rotate one full time is what we call a day.  On Earth, it takes 365 days (a year) to orbit the sun, and 24 hours to rotate (a day).  There are seven other full planets in our solar system.

The sun and the 8 planets of our solar system.  You can see the order and sizes of the planets.

The four planets closest to the sun are the terrestrial planets.  They have a rocky surface, and the four farther planets are mostly gas.

Mercury is closest to the sun, and it is about the size of our moon (small).  It is very hot especially on the day side of the planet, facing the sun.  It gets to about 840 degrees F!  But it also gets cold on the night side, facing away from the sun, way below freezing!  That's because it doesn't have an atmosphere, which helps keep heat in and protects the planet.  There are lots of craters all over it, and nothing can live there.  It takes 88 days for Mercury to orbit the sun, and a day lasts 59 Earth days!

This is a picture by one of the probes that looked at Venus

Venus is the second planet, and it is actually hotter than Mercury because of the runaway greenhouse effect.  It has an atmosphere of carbon dioxide and sulfuric acid, and very high pressure.  Two probes were sent to look at Venus and they both lasted only an hour before they were destroyed by the conditions.  It takes Venus 225 days to orbit the sun, and 243 days to rotate one time.  Venus rotates in the opposite direction of the other planets and very slowly, because a very long time ago a giant chunk of space debris called a planetesimal hit it very hard.

Earth, the third planet, has a surface that is 2/3 liquid water, which is why it looks blue.  It has an atmosphere of mostly nitrogen and oxygen.  These two things are very important for allowing life to exist.  Earth has one moon that orbits it, and we'll talk about how scientists think the moon was formed!

This shows Olympus Mons compared to Earth's tallest mtns.

Mars is called the red planet because it looks reddish; the red color comes from the iron, like rust.  Mars has a really high mountain on it, called Olympus Mons, which is about 3 times larger than Mount Everest (Earth's tallest mountain).  There's no such thing as Martians, but people are still looking at whether maybe life existed on Mars in the past.